Sterilizer



A. L. JONES ET AL 3,351,422

STERILIZER Filed Feb. 9, 1962 4 Sheets-Sheet 1 INVENTORS ARTHUR LJoNE-sand EUGENE J. NEALJJR.

ATTORNEYS Nov. 7, 11967 A. L. JONES ET AL STERILIZER 4 Sheets-SheetFiled Feb. 9, 1962 New, 7, W7

STERILIZER Filed Feb. 9

4 Sheets-Sheet 5 S m E 9 m s w 8 V 35 m m K E A W. P LT 1 T 3 5 TG R U IAE 7Q n a n 1- 0 l O :L 2

BY WWW ATTO EYS A. L. JONES ET AL Nov. 7,1967

STERILIZER 4 Sheets-Sheet 4' Filed Feb. 9, 1962 ARTHUR. LJoNEs and.EuqENE J. NEAL,J2., INVENTORS ATTOR N E Y5 United States Patent Otitice3,351,422 Patented Nov. 7, 1967 3,351,422 STERELHZER Arthur L. Jones andEugene J. Neal, Jr., Charlotte, N.C., assignors to The Pelton & CraneCompany, Charlotte, NAB a corporation of North Carolina Filed Feb. 9,N62, Ser. No. 172,208 5 Claims. (Cl. 21-94) The present inventionrelates generally to an apparatus for sterilizing dental and medicalarticles and supplies, such as instruments, glassware, dressings and thelike. More particularly, the persent invention is directed to asterilizer having a sterilizing chamber in which sterilization of sucharticles and supplies can be accomplished by utilizing either steamunder pressure or dry heat as a sterilizing agent.

Heretofore, two different types of apparatuses have been employed forrespectively sterilizing objects by steam under pressure and bysustained dry heat at high temperatures. As between these two modes ofsterilizing procedure, it is generally agreed that steam under pressureis to be preferred as a sterilizing agent, because sterilization bysteam under pressure can be accomplished at lower temperatures and in ashorter period of time than is required to effect sterilization by dryheat. However, in certain instances, dry heat sterilization offersadvantages over steam sterilization, such as in the sterilization ofmetallic instruments, glassware, and other heatresistant articles whichmust be completely dry during the sterilization. Metallic instrumentsare commonly made of carbon steel which will corrode to some extent whencontacted by steam. Where the carbon steel instrument is of a type usedfor cutting, its blade must be kept in an extremely sharp condition-acondition difficult to maintain if the instrument is sterilized by steamwhich has a tendency to cause the blade to be dulled because of thecorrosive effect of the steam. Sterilization of glassware by steam underpressure frequently results in objectionable etching of the glassware.Thus, dry heat sterilization has been found to be more practical anddesirable than sterilization by steam under pressure in instances wherethe articles to be sterilized are of a type likely to be adverselyaffected by the steam even though dry heat sterilization requires dryheat at a high temperature sustained over a comparatively long period oftime. Thus, separate and distinct sterilizers respectively relying uponsteam under pressure and dry heat as a sterilizing agent are commonamong the medical or dental equipment found in hospitals, clinics andindividual offices of doctors and dentists.

A single dual-purpose sterilizing apparatus equipped for either steamsterilization or dry heat sterilization treatments of articles to besterilized has been previously regarded as being impractical. In thelatter respect, heretofore an efficient control system for synchronizingthe variable factors involved in utilizing steam pressure or dry heat asa sterilizing agent in a single dual-purpose sterilizer and having thevirtues of simplicity of construction, ease of operation, and rapidresponse has not been devised.

Moreover, the problem of obtaining rapid response toward achieving aminimum sterilizing pressure and/ or temperature in a single sterilizerregardless of Whether the sterilizing medium may be steam under pressureor sustained dry heat has not been satisfactorily resolved. Rapidresponse toward raising the temperature and pressure within asterilizing chamber partially filled with Water to satisfactory levelsfor achieving steam sterilization can best be accomplished by applyingconcentrated heat capable of producing extremely high temperatures tothe water within the sterilizing chamber. On the other hand,concentrated heat capable of producing extremely high temperatures islikely to overheat the sterilizing chamber and the articles therein tobe sterilized to a harmful degree when the sterilizing chamber isemptied of water and steam in an instance where dry heat is to beemployed as the sterilizing medium. Rapid response in achieving aminimum dry heat sterilizing temperature as quickly as possible musttherefore be: conditioned upon certain limitations imposed by safetyfactors on the concentration and quantity of heat supplied to thesterilizing chamber to avoid harmful overheating of the sterilizingchamber and the artic1:s therein to be sterilzed.

It s also important to provide a hermetically sealed sterilizing chamberin accomplished steam sterilization for permitting a pressure build-upin the chamber upon the admission of steam thereto or the generation ofsteam therein. A relatively massive pressure door is therefore normallyemployed to hermetically seal the opening to the chamber through whicharticles to be sterilized are admitted into the chamebr when steam underpressure is employed as the sterilizing medium to withstand thesuperamospheric pressure developed in the chamber. The use of arelatively massive door for hermetically closing the sterilizingchamber, considered desirable from a safety standpoint in sterilizersemploying steam under pressure as a sterilizing medium, detracts fromthe rapidity at which the temperature in the interior of the sterilizingchamber will rise to a degree suflicient to effect sterilization by dryheat. In this respect, the mass of the door absorbs heat from thechamber walls and the interior of the chamber to significantly slow downthe rate of temperature rise within the interior of the chamber. Each ofthe above-mentioned factors have contributed to the general belief thatseparate sterilizers for steam and dry heat sterilization are necessary,if it is desired to elficiently accomplish sterilization treatments byrelying upon either steam under pressure or dry heat as a sterilizingagent.

Accordingly, it is a primary object of this invention to provide animproved dual-purpose sterilizer having a chamber in which sterilizationcan be accomplished by utilizing either steam under pressure or dry heatas a sterilizing agent, thereby eliminating the added expense ofequipping medical and dental facilities with separate sterilizer unitsfor respectively performing sterilization procedures by steam underpressure and dry heat.

It is another object of this invention to provide an improveddual-purpose sterilizer having a sterilizing chamber for accomplishingsterilization of dental and medical articles and supplies by employingeither steam under pressure or dry heat as the sterilizing agentdepending upon the circumstances, wherein a plurality of heatingelements are arranged in proximity to the chamber walls for heating thechamber walls with energization of the heating elements being regulatedby a Selective heater control means operative to energize a singleheating element of the plurality of heating elements during a steamsterilization cycle, while energizing the plurality of heating elementsunder a reduced power input for each heating element during a dry heatsterilization cycle as compared to the power input selectively directedinto the single heating element so as to substantially eliminate anypossibility of damage to the sterilizer caused by overheating of thechamber walls or other components of the sterilizer when the chambercontains no water or an insignificant amount thereof. In this way, thedual-purpose sterilizer responds rapidly in producing pressures and/ ortemperatures within its sterilizing chamber at levels sulficient toeffect sterilization by steam or dry heat, while maintaining a saferestriction on the concentration and quantity of heat developed by theplurality of heating elements during a dry heat sterilization cycle.

It is another object of this invention to provide an improveddual-purpose sterilizer having a chamber in which dental and medicalarticles and supplies may be placed for sterilization by steam underpressure or by dry heat depending upon the circumstances, wherein theopening into the chamber through which the articles and supplies to besterilized are inserted is adapted to be closed by interchangeableclosures subject to the mode of sterilization employed. In the latterconnection, a relatively massive pressure door is employed as a closureto hermetically seal the chamber against pressure leakage when steamunder pressure is employed as the sterilizing agent, while an auxiliaryclosure is provided in the form of a lightweight door of limited masswhich can be quickly heated when employed as a closure for the chamberduring a dry heat sterilizing cycle to speed up the response of thesterilizer in attaining a temperature within the chamber of sufficientmagnitude to effect sterilization by dry heat.

Some of the objects of the invention having been stated, other objectswill appear as the description proceeds when taken in connection withthe accompanying drawings, in which:

FIGURE 1 is a perspective view of the improved sterilizer in accordancewith the present invention, and showing a closure in the form of arelatively massive pressure door hermetically sealing the opening intothe sterilizing chamber for performing a sterilizing treatment withsteam under pressure as the sterilizing agent;

FIGURE 2 is a perspective view similar to FIGURE 1, but showing anauxiliary closure in the form of a lightweight lid or door of limitedmass covering the opening into the sterilizing chamber with the hermeticdoor closure of FIGURE 1 being disposed in an open position forperforming a sterilizing treatment with dry heat as the sterilizingagent;

FIGURE 3 is an enlarged perspective view of the auxiliary lightweightlid or door shown in FIGURE 2, looking at the inwardly disposed sidethereof hidden from view in FIGURE 2;

FIGURE 4 is an enlarged plan view of the sterilizer as shown in FIGURE 1with the top wall of the outer housing or cabinet being removed forpurposes of clarity;

FIGURE 5 is an enlarged elevational view of the sterilizer as shown inFIGURE 1, looking at the right side thereof and with the hermetic doorclosure and the right side wall of the outer housing or cabinet beingremoved for purposes of clarity;

FIGURE 6 is an enlarged vertical sectional view taken along the line 6-6in FIGURE 1;

FIGURE 7 is a schematic wiring diagram illustrating the selective heatercontrol means for the electrical circuits energizing the heatingelements employed in the sterilizer; and

FIGURE 8 is a schematic view illustrating the piping systeminterconnecting various components of the sterilizer for transmittingfluid to and from the sterilizing chamber.

Referring more specifically to the drawings, the sterilizer has an outercasing or housing forming a cabinet 10 in which a sterilizing chamber 11is received. The bottom of the cabinet 10 is provided with foursupporting feet 18 which are preferably made adjustable as to theirlength by suitable means (not shown) for raising and lowering thesterilizer cabinet 10 as may be required to tilt the sterilizing chamber11 as desired or to accommodate the cabinet 10 in a particular location.Provision may also be made for adjusting the front pair of feet 18longitudinally along the bottom of the cabinet 10 by means (not shown)to accommodate the cabinet 10 in locations of varying depth. The chamber11 is generally cylindrical and includes an integral rear end closure,access to the chamber 11 being afforded through its open front end. Thechamber 1 11 is mounted within the cabinet 10 so that its open front endcoincides with a circular opening provided in the front wall of thecabinet 10 to which the open front end of the chamber 11 is connected.An annular liner 12 (FIGURE 6) is suitably secured to the open front endof the chamber 11, as by welding, the annular liner 12 beingfrictionally received within the opening provided in the front wall ofthe cabinet 10. A door 13 of generally circular configuration conformingto the shape of the opening through the front wall of the cabinet 10 andthe open front end of the chamber 11 is mounted on the front wall of thecabinet 10 by means of an integral bar 20 hingedly connected to thecabinet 10 for pivotal movement of the door 13 between positions openingand closing the chamber 11. It will be understood that the door 13 is arelatively massive pressure door of a type regarded as a suitableclosure for a sterilizing chamber in which sterilization by steam underpressure will be employed. The door 13 is provided with a resilientpressure-responsive annular sealing gasket 14 made of suitableheat-resistant material, such as silicone rubber. The gasket 14 isadapted to sealingly engage the liner 12 when the door 13 is in closedposition, thereby cooperating with the door 13 to provide a hermeticpressure-tight closure for the open front end of the chamber 11. Whensteam sterilization is in progress within the chamber 11, the door 13 islatched in closing relation to the front end of the chamber 11 forhermetically sealing the chamber 11 by means of a bolt 15 slidablymounted within the bar 20 of the door 13 and receivable by a keeper 16mounted on the front wall of the cabinet 10 (FIGURES 1 and 2). The bolt15 is manipulated between positions latching and unlatching the door 13by a handle 17 afiixed thereto, the handle 17 being readily grasped forsliding the bolt 15 into and out of reception with the keeper 16. Inthis respect, it will be observed that the bar 20 is suitably slottedfor slidable movement of the bolt 15 and its attached handle 17, therebeing a depending slotted section for reception of the handle 17 whenthe free end of the bolt 15 has been moved within the keeper 16. It willbe understood that the handle 17 when disposed in vertical alinementwith the depending slotted section in the bar 20 may be drawn downwardlyin an arcuate movement rotating the bolt 15, wherein the handle 17 willbe retained Within the depending slotted section against inadvertentmovement sliding the bolt 15 out of the keeper 16 to unlatch the door13.

The door 13 defines a hermetic closure for the open front end of thechamber 11 and is complemented by a non-hermetic auxiliary closure inthe form of a lightweight lid or auxiliary door 21 which is utilized toclose the chamber 11 when dry heat sterilization is in progress Withinthe chamber 11 rather than steam sterilization. The auxiliary door 21 isof limited mass as compared to the relatively massive pressure door 13and can be quickly heated to speed up the response of the sterilizer inattaining a temperature within the chamber 11 of sufficient magnitude toeffect sterilization by dry heat. As shown best in FIGURE 3, theauxiliary door 21 comprises inner and outer circular discs 22, 23respectively, the inner disc 22 having a diameter substantially greaterthan the outer disc 23. The outer disc 23 is secured to the inner disc22 in superimposed spaced relationship over the central portion thereofby suitable fastener means, such as studs 24, 24 extending therebetween.The diameter of the inner disc 22 is slightly greater in size than theopening through the front cabinet wall and the open front end of thechamber 11 to provide a marginal portion on the auxiliary door 21overlying the portion of the front cabinet wall defining the boundary ofthe circular opening therethrough. The auxiliary door 21 is releasablymounted in a position closing the open front end of the chamber 11 withthe larger inner disc 22 thereof covering the open front end of thechamber 11 and loosely held in place by means of a plurality of holdingbrackets 25 secured to the inwardly disposed surface of the inner disc22. Each of the holding brackets 25 includes a lip extendingtransversely from the inner surface of the inner disc 22 and adapted tobe loosely received within the annular liner 12 forming the mouth of theopening in the front end of the chamber 11.

It will be observed that one of the holding brackets 25 also has anintegral retainer tab member 26 connected to the lip thereof andextending in spaced generally parallel relation to the inner surface ofthe inner disc 22. In closing the open front end of the chamber 11, theauxiliary door 21 is initially arranged with respect to the chamberopening so as to admit the portion of its inner disc 22 carrying theholding bracket 25 provided with the tab member 26 within the chamber11. The tab member 26 is disposed behind the annular liner 12 andtogether with the lips on the other holding brackets 25 which areadapted to loosely bear against the inner periphery of the annular liner12 retains the auxiliary door 21 in a position closing the chamber 11. Athermometer 27 for measuring the temperature attained in the chamber 11during a dry heat sterilization cycle is carried by the inner disc 22 ofthe auxiliary door 21, the opposite ends of the thermometer 27protruding outwardly and inwardly of the auxiliary door 21,respectively. The exposed portion of the thermometer 27 extendingoutwardly of the auxiliary door 21 permits visual observation of the dryheat temperature within the chamber 11. The bulb end of the thermometer27 which protrudes within the chamber 11 is preferably shielded fromdamage by a perforated guard or cage 28. The cage 28 is afiixed to theinner surface of the inner disc 22 and encircles the inwardly protrudingportion of the thermometer 27 in spaced relationship therewith to permitfree flow of air about the thermometer 27 for obtaining reliablemeasurements of temperature within the chamber 11. In instances wherethe case 28 may be responsible for absorbing some of the heat from theinterior of the chamber 11 and allowing heat dissipation through theinner disc 22 to cause a temperature reduction in the space between thethermometer 27 and the cage 28, it has been found practical to employ acalibrated thermometer with an offset graduated scale compensating forthe heat loss caused by the protective cage 28 for the thermometer 27.Thus, the temperature reading registered on such a calibratedthermometer will coincide with the actual temperature within the chamber11 even though the heated air in direct contact with the bulb of thethermometer 27 is at a lower temperature than the actual temperaturewithin the chamber 11 because of the heat loss caused by the cage 28.For convenience in mounting and removing the auxiliary door 21, a handle29 (FIGURE 2) is provided on the outer disc 23 of the auxiliary door 21.Heat is transmitted to the inner disc 22 of the auxiliary door 21 fromthe rising heat of the chamber walls and the rising heat within thechamber 11 in attaining a high temperature within the chamber 11 duringdry heat sterilization. However, the outer disc 23 and the handle 29afiixed thereto will remain relatively cool because of the spacedrelationship between the inner and outer discs 22, 23 of the auxiliarydoor 21 which effectively thermally isolates the outer disc 23 and thehandle 29 from the inner disc 22. This thermal isolation of the outerdisc 23 and the handle 29 allows the auxiliary door 21 to be immediatelyremoved from the front cabinet wall to open the chamber 11 following adry heat sterilization cycle without danger of personal injury fromburns due to the high temperature employed in this mode ofsterilization. The chamber 11 is thereby permitted to cool more readilyby exposing its interior to ambient temperature conditions in thevicinity of the sterilizer soon after the dry heat sterilization cyclehas been completed.

Means are provided to heat the chamber walls for raising the temperaturetherewithin in processing the sterilization of articles disposed Withinthe chamber 11 by steam under pressure or by dry heat. In thisc0nnection, the heating means comprises a plurality of electric heatingelements 30 (FIGURES 6 and 7). The heating elements 30 are disposedbeneath the bottom portion of the cylindrical chamber 11 in clampedengagement therewith, as will be herein-after described. Referring toFIG- URE 7, it will be observed that each of the heating elements 30comprises an elongated curved plate having electrical resistance wiringembedded therein and conforming to the cylindrical shape of the chamberwalls, there being a centrally disposed heating element 30 and a pair ofside heating elements 30, 3t] flanking the centrally disposed heatingelement 30. As will be described hereinafter, the plurality of heatingelements 30 are thermostatically controlled and in addition are adaptedto be energized by manually-controlled electric heating circuits so asto provide for selective energization of the centrally disposed heatingelement 30 at an increased power input while the side heating elements30, 30 remain inactive during a steam sterilization cycle and to providefor simultaneous energization of the plurality of heating elements 30 ata reduced power input during certain time intervals preceding andfollowing the steam sterilization cycle and during a dry heatsterilization cycle. Thus, it is contemplated that the side heatingelements 30, 30 will operate only under a reduced power input, while thecetnrally disposed heating element 30 will be selectively energizedunder high and reduced power inputs. Heating element-s of the electricalresistance wire type may develop one or more hot spots along the lengthof the wire. Since the central heating element 30 is intended to beselectively energized under a high power input during the steamsterilization cycle, any such hot spots developed in the electricalresistance wiring thereof may be capable of creating suflicient-ly largeheat differentials along certain areas of the chamber walls when thecentral heating element 39 is energized under a high power input tocause buckling of the chamber walls. This problem of buckling isaccentuated in instances where the chamber 11 is in a tilted positionduring a steam sterilization cycle so as to cause any water therein tocollect at one end or the other, and a hot spot on the central heatingelement 30 happens to occur in proximity to a portion of the bottomchamber wall above the water level in the chamber 11. For this reason, aheat equalizer plate 30a is preferably sandwiched between the cent-rallydisposed heating element 3t} and the bottom wall of the chamber 11 toevenly distribute heat emanating from the central heating element 30along the bottom wall of the chamber 11. The heat equalizer plate 30a isappropriately curved to correspond to the curvature of the centralheating element 30 and the cylindrical shape of the bottom wall of thechamber 11 and is made of a material possessing excellent heatconductivity, such as aluminum, to enable it to disperse the effect ofany hot spots on the central heating element 30 throughout its surfacearea adjoining the bottom wall of the chamber 11, thereby avoiding thetroublesome consequences associated with such hot spots.

The plurality of heating elements 3 0 are releasably clamped against thechamber walls (with the heat equalizer plate 30a interposed between thecentral heating element 30 and the bottom portion of the chamber walls)by a clamping plate 301; (FIGURE 6) overlying the heating elements 30and a plurality of suitably adjustable straps 31 (FIGURE 4) encirclingthe chamber 11 and the clamping plate 3% to firmly hold the heatingelements 30 in place about the lower opposite side portions and bottomportion of the chamber walls for transmitting heat thereto.

A water supply for the chamber 11 from which steam is to be generated ineifecting the sterilization of objects placed in the chamber 11 by steamunder pressure is obtained from a reservoir tank 32 (FIGURES 4, 5 and8). The reservoir tank 32 is mounted Within the cabinet 16 to one sideof the chamber ill, the reservoir tank 32 being cylindrical andextending vertically upward from the bottom wall of the cabinet 10.Within the reservoir tank 32, there is a coiled condenser tube 331 forcondensing steam discharged from the chamber 11 at the conclusion of asteam sterilization cycle to replenish the water supply in the reservoirtank 32. A drain plug 34 is provided in the bottom wall of the reservoirtank 32 and is accessible from the bottom wall of the cabinet 10 (FIGUREto drain water from the reservoir tank 32 when it is desired to cleanthe interior of the reservoir tank 32 and the condenser tube 33contained therein. It will be noted that the top wall of the cabinetincludes a circular aperture in vertical alinement with the reservoirtank 32 to permit filling of the reservoir tank 32 to a graduated fillline 35 (FIGURE 5) for replenishing water in the tank 32 lost byevaporation. The reservoir tank 32 is provided with a ventilated cover36 (FIGURES 1 and 2) loosely received within the aperture formed in thetop wall of the cabinet 10 and mounted atop the reservoir tank 32.

It will be observed that a tray 37 is mounted within the chamber 11 soas to extend lengthwise in spaced relation above the bottom thereof. Inthis respect, the tray 37 is fastened to an upright support member 38projecting from the bottom wall of the chamber 11 adjacent the mouththereof defined by the annular liner 12 by suitable means, such as screw39, and is further supported above the bottom wall of the chamber 11 bya transverse band 3% extending between the side walls of the chamber 11and beneath the rear portion of the tray 37 (FIGURE 6). The tray 37 hasan indicator bracket 40 afiixed therebeneath. The indicator bracket 40is disposed at the forward end of the tray 37 and is provided with afill plate 41 integral therewiththe fill plate 41 being horizontallyarranged in spaced relation between the tray 37 and the bottom of thechamber 11. As shown in FIGURE 8, the tray 37 has a plurality ofperforations therein to allow steam generated from Water in the chamber11 below the tray 37 to pass upwardly through the perforations in thetray 37, and the forward end of the tray 37 is recessed to expose thefill plate 41 which is visible through the open front end of the chamber11.

Referring now to the piping system in the sterilizer for admitting waterinto the sterilizing chamber 11 and thereafter discharging steam fromthe chamber 11 following the conclusion of a steam sterilization cycleas schematically illustrated in FIGURE 8, the passage of fluid to andfrom the chamber 11 is manually regulated by a rotatable control knob 42which also simultaneously regulates the energization of the heatingelements 30 as will be subsequently described. The control knob 42 ismounted on a control panel 43 forming a part of the front wall ofcabinet 10, the control knob 42 being the lower knob in a vertical rowof three knobs disposed on the control panel 43, as shown in FIGURE 1.The control knob 42 has a spindle 44 extending through the control panel43, and the spindle 44 carries a pair of spaced apart cam members 45, 46which are adapted to actuate a valve control mechanism 47 regulatingfluid flow in the piping system, while also actuating a pair of switchesin regulating energization of the heating elements 30. In this respect,it will be observed that each of the cam members 45, 46 has a bluntprotrusion for depressing respective flexible follower members 50, 51associated therewith. The valve control mechanism 47 comprisesplunger-operated valve members A and B mounted within a valve housing52, each of the valve members A, B being selectively actuated by meansof the cam members 45, 46 and the flexible follower members 50, 51thecam member and follower member 50 being effective to depress a plungermoving valve member A to an open position and the cam member 46 andfollower member 51 similarly depressing a plunger to move valve member Bto an open position when the control knob 42 is disposed in selectedposition. Ports 53, 54, and are provided in the valve housing 52-port 53communicating with the valve chamber corresponding to valve member B ata point above valve member B, port 54 communicating with the valvechambers corresponding to both valve members A, B at points below thevalve members A, B, and port 55 communicating with the valve chambercorresponding to valve member A at a point above valve member A.

When the control knob 42 is in the off position illustrated in FIGURE 8,both valve members A, B will be in closed positions to blockcommunication between the chamber 11 and the reservoir tank 32. Uponrotating the control knob 42 in a counter-clockwise direction to thefill position, the cam member 46 will be arranged so as to depress thefollower member 51 associated therewith for moving the valve member B toan open position which connects ports 53 and 54 through the unblockingof the valve chamber containing valve member B. Water is thereby allowedto flow from the reservoir tank 32 through a delivery tube 56 extendingfrom the reservoir tank 32 near the bottom thereof, into port 53, pastthe open valve member B into port 54, and a conduit 57 which leads tothe bottom of chamber 11 adjacent the front end thereof at a pointdisposed beneath the fill plate 41. Water from the reservoir tank 32 isadmitted to the chamber 11 through the conduit 57 until the fill plate41 is covered by the water.

When the water within the chamber 11 has reached a level covering thefill plate 41, the control knob 41 is then turned to sterilize positionwhich causes valve 1 member B to return to closed position by movementof the cam member 46 so as to discontinue its depressing action on thefollower member 51. Valve member A is also in closed position at thesterilize position of the control knob 42 which isolates the chamber 11from the reservoir tank 32 during a steam sterilization cycle and stopsthe flow of water into the chamber 11. Upon rotating the control knob 42to the vent position, the cam member 45 will be arranged so as todepress the follower member 50 for moving the valve member A to an openposition, while valve member B remains in a closed position. Themovement of valve member A to an open position connects ports 54 and 55through the unblocking of the valve chamber containing valve member A.Steam and water within the chamber 11 are thereby allowed to bedischarged from the chamber 11 through the conduit 57, into port 54,past the opened valve member A into port 55, and to a discharge tube 6%)which leads back into the reservoir tank 32 through the condenser tube33, the upper end of the condenser tube 33 being connected to thedischarge tube 60. A suitable thermostatic air valve 61 is associatedwith the discharge tube 60 adjacent the connection between the dischargetube 60 and the condenser tube 33. The thermostatic air valve 61 isintended to release air having a relatively low temperature from thechamber 11 into the condenser tube 33 by allowing the low-temperatureair from the chamber 11 to be passed into the portion of the dischargetube 60 linking the thermostatic air valve 61 with the condenser tube 33in a manner to be presently described. A safety relief valve 62 isassociated with the thermostatic air valve 61 by a connecting conduit 63so as to protect the chamber 11 against an excessive pressure build-uptherein, the pressure relief valve 62 being of a type which may beadjustably set to open when a predetermined excessive pressure exists inthe chamber 11 for exhausting the excessive pressure into the reservoirtank 32 through an exhaust tube 64 providing communication between thesafety relief valve 62 and the upper portion of the reservoir tank 32.The chamber 11 communicates with the thermostatic air valve 61 and thesafety relief valve 62 through an air tap line 65 which is connected atone end to the rear wall of the chamber 11 at a point beneath the tray37 (FIGURE 6) and at its other end to the connecting conduit 63extending between the thermostatic air valve 61 and the safety valve 62.It will be understood that the thermostatic air valve 61 may be adjustedso as to automatically close whenever a predetermined temperature isattained in the chamber 11 during a steam sterilization cycle. Until thepredetermined temperature is attained in the chamber S 11, thethermostatic air valve 61 remains open to allow relativelylow-temperature air to be forced out of the chamber 11 as steam is beinggenerated therein through the air tap line 65, the portion of theconnecting cnduit 63 linking the air tap line 65 to the thermostatic airvalve 61, through the open thermostatic air valve 61 and into thecondenser tube 33 via the portion of the discharge tube 60 linking thethermostatic air valve 61 to the condenser tube 33. In this way, thepredetermined steam sterilizing pressure will not begin to build up inthe chamber 11 to an appreciable extent until the chamber 11 is filledwith relatively high temperature steam which assures that proper steamsterilizing temperatures will be quickly obtained in the chamber 11. Inpractice, the thermostatic air valve 61 will open and closeintermittently throughout the duration of a steam sterilization cycleeven after the predetermined temperature at which the thermostatic airvalve 61 has been set to close has been attained in the chamber 11because of the heat loss eventually sustained by the mixture of air andsteam temporarily trapped in the air tap line 65 and the portion of theconnecting conduit 63 linking the air tap line 65 to the thermostaticair valve 61 when the thermostatic air valve 61 is closed. The coolingof this trapped air-steam mixture below the predetermined temperaturecauses the thermostatic air valve 61 to open, but soon after thethermostatic air valve 61 has opened to bleed off the cooled air-steammixture, it closes upon being subjected to a fresh air-steam mixtureissuing from the chamber 11 which is at or above the predeterminedtemperature required to close the thermostatic air valve 61. Anyexcessive pressure build-up in the chamber 11 over the predeterminedsuperatmospheric pressure desired will be exhausted from the chamber 11through the air tap line 65 and the conduit 63 into the reservoir tank32 by the opening of the safety relief valve 62 in the manner previouslydescribed.

A thermometer 66 is installed in the air tap line 65 for measuring thesteam temperature within the chamber 11, the thermometer 66 beingconnected to a temperature gauge 67 for visibly registering the steamtemperature within the chamber. The steam pressure within the chamber 11is visibly indicated on a pressure gauge 70, the steam pressure withinthe chamber 11 being communicated to the pressure gauge 76 by means ofthe air tap line 65 and a branch pressure line '71 connected to thepressure gauge 70 and the air tap line 65. The temperature gauge 67 andthe pressure gauge 76 are mounted in the front wall of the cabinet so asto be readily observed, as shown in FIGURES 1 and 2.

Referring now to FIGURE 7, which schematically illustrates the electricheating circuits and the control means for selectively directingelectric current to the plurality of heating elements 30, it will beobserved that the control knob 42 and the cam members 45, 46instrumental in regulating the flow of fluid between the reservoir tank32 and the chamber 11 also simultaneously effect the selectiveenergization and the de-energization of the heating elements 30. It willbecome ap parent as the description proceeds that each of the pluralityof heating elements 30 is energized under a low power input when theknob 42 is located in the full and vent positions, while the centrallydisposed heating element 30 is selectively energized under an increasedpower input with the side heating elements 36, 30 being inactive whenthe control knob 42 is located in the sterilize position. A pair offlexible follower elements 72, 73, separate and distinct from theflexible follower members 50, 51 previously discussed in connection withthe regulation of the passage of fluid in the piping system of thesterilizer, are respectively associated with the cam members 45, 46 foreffecting the operation of switches 74 and 75. Switch 74 is a primaryheating circuit switch comprising a pivotal arm movable between acircuitbreaking position in which the delivery of electric current tothe three heating elements 30 is cut off and a position in engagementwith a fixed contact 76 in which the delivery of electric current to allthree of the heating elements 36 or to only the centrally disposedheating element 30 is assured, subject to the operation of a modulationthermostat as will be later described. Switch 75 is a selectivesecondary heating circuit switch determining whether all three of theheating elements 30 or only the centrally disposed heating element 30will be energized when the primary heating circuit switch 74 is closedto engage the fixed contact 76. The selective secondary heating circuitswitch 75 comprises a pivotal arm movable between a position inengagement with a fixed contact 77 in which electric current will bedirected to all three of the heating elements 30 and a position inengagement with a fixed contact 78 in which electric current will beselectively directed to the centrally disposed heating element 30. Itwill be understood that the blunt protrusions on the cam members 45 and46 depress the fiexible follower elements 72 and 73 in a predeterminedsequence depending upon the position of the control knob 42 foroperating the switches 74 and 75. As illustrated diagrammatically inFIGURE 7, each of the pivotal arms of the switches 74, 75 is providedwith a button intermediate its ends against which the follower elements72, 73 correspondingly bear, the switch arms pivoting in response toappropriate movement of the cam members 45, 46 either disposing theblunt protrusions thereon in contact or out of contact with the followerelements 72, 73. Suitable means, such as springs (not shown) bias thepivotal arm of switch 74 into engagement with the fixed contact 76 andthe pivotal arm of switch 75 into engagement with the fixed contact 77on occasions when the blunt protrusions of the cam members 45, 46 areout of contact with the follower elements 72, '73.

Current to the heating elements 30 is also controlled by means of amodulating thermostat 86 which is ar ranged in series with the primaryheating circuit switch 74. The thermostat 80 comprises an elongatedtemperature-sensing bulb 81 disposed within the chamber 11 beneath thetray 37 and the level of the fill plate 41 depending therefrom so as tobe normally immersed in Water received in the chamber 11 (FIGURE 6). Thetemperature-sensing bulb 81 is connected to a rotatable control knob 82mounted on the control panel 43 of the cabinet 10 above the control knob42. The control knob 82 may be rotated to adjust the thermostat 86 forcutting off and turning on the electric current to the heating ele ments36 when the temperature within the chamber 11 cycles above and below adesired level. In the latter connection, when the temperature within thechamber 11 is at or below the level determined by a particular settingof the control knob 82, electric current is allowed to pass bet-weenspaced terminals 83 and 84 of the thermostat 80 completing a primaryheating circuit including the closed switch '74. Should a temperaturebuild-up above the predetermined level occur in the chamber 11, noelectric current will pass between the thermostat terminals 83, 84 whilethis excessive temperature condition is present, thereby breaking theprimary heating circuit and interrupting the delivery of electriccurrent to the heating elements 30. The control knob 82 may be rotatedin either a clockwise or counterclockwise direction for adjusting thethermostat 80 to operate during a dry heat sterilization cycle or asteam sterilization cycle, respectivelythere being suitable indicia onthe control panel 43 behind the control knob 82 divided into dry heatsterilization and steam sterilization sectors for identifyinig where anindicator mark on the control knob 82 should be located to correspondwith the mode of sterilization employed.

Upon supplying power to the sterilizer by connecting a suitably groundedelectrical plug 96 into a convenient power outlet electric current willbe deliverd to all three heaters 30 when the control knob 42 is rotatedfrom the off to the fill position. The fill position of control knob 42arranges the cam member 45 so as to allow the arm of switch 74 to engagethe contact 76, while the arm of switch 75 remains in engagement withthe contact 77, thereby completing an electrical circuit passing througheach of the three heating elements 39. As shown in FIG- URE 7, thiselectrical circuit includes the delivery of electric current from oneplug terminal through a quick connector junction W, across the pivotalswitch arm '74 which is in engagement with the contact 76 in the fillposition, across the thermostat terminals 83, 84-, across the pivotalswitch arm 75 which is in engagement with the contact 77 in the fillposition, through a quick connector junction X, and then proceedingthrough the three heating elements 30 which are serially connected so asto direct current flow through one of the side heating elements, theother side heating element and finally through the centrally disposedheating element, from where the current is directed through a quickconnector junction Y and is returned to the other plug terminal.

The same electrical circuit just described which provides for theenergization of all three heating elements 30 will also be completedwhen the control knob 42 is disposed in the vent position, since thepivotal arm of switch 74 will be in engagement with the contact 76 andthe pivotal arm of switch 75 will be in engagement with the contact 77.In the sterilize position of the control knob 42, while the pivotal armof the primary heating circuit switch 74 engages the contact 76, it willbe observed that the blunt protrusion on the cam member 46 will bedisposed so as to depress the follower element 73 for moving the pivotalarm of the secondary heating circuit switch 75 away from the contact 77and into engagement with the contact 78. Thus, when a steamsterilization cycle is in progress within the chamber 11, the centralheating element 39 is selectively energized under an increased powerinput by engagement between the switch arm 75 and the contact 78, whilethe side heating elements 30 are inactivated. In this respect, theelectric circuit which is formed in the sterilize position of thecontrol knob 42 is the same as that previously described which is formedin the fill and vent positions of the control knob 42 except for theportion controlled by the location of the switch arm 75. At sterilizeposition, the electrical circuit extends across the pivotal switch arm75 in engagement with the contact 78, through a quick connector junctionZ, and then proceeds through the centrally disposed heating element 30only, the quick connector junction Y, and returns to the other plugterminal.

A safety cut-off thermostat 91 is interposed in the wiring connectingthe quick connector junction Z to one terminal of the centrally disposedheating element 30. The safety cut-off thermostat 91 may be adjustablyset to cut olf the electric current and break the electrical circuitselectively energizing the centrally disposed heating element 30 shouldthe temperature of the central heating element 39 increase to apredetermined excessive degree when the control knob 42 is located inthe sterilize position during a steam sterilization cycle. While thesafety cut-off thermostat 91 may be made directly responsive to thetemperature of the central heating element 30, it is preferred to makethe safety cut-off thermostat 91 directly responsive to the temperatureof the heat equalizer plate 300:, in which case the safety cut-offthermostat 91 will be indirectly responsive to the temperature of thecentral heating element 30. To this end, the heat equalizer plate 39a isprovided with an integral depending flange 94 (FIGURE 7) extending belowthe central heating element 30, and the safety cut-off thermostat 91includes a thermally-sensitive circuit-breaking arm 95 in associationwith a pair of switch arms 96, 97 having normally engaging electricalcontacts. The switch arms 96, 97 are respectively connected in thewiring leading from the quick connector junction Z to one terminal ofthe central heating element 30 so as to cut off the electric currentselectively energizing the central heating element 30 should theirelectrical contacts become disengaged. The safety cut-off thermostat 91is mounted on the depending flange 94 of the heat equalizer plate 30a bysuitable means, such as an insulated threaded bolt 98 extending throughthe switch arms 96, 97 and the circuit-breaking arm 95 of the safetycut-otf thermostat 91 and through the depending flange 94, with thethermally-sensitive circuit-breaking arm 95 being adjacent the dependingflange 94. It will be observed that the switch arm 97 is shorter inlength as compared to the switch arm 96 and the circuit-breaking arm 95and is located therebetween, while the circuit-breaking arm 95 carries anon-conductive prong 99 which abuts the switch arm 96 and is disposedbeyond the shorter switch arm 97. Thus, when the central heating element30 acquires a predetermined excessive degree of temperature, thisexcessive temperature will be transmitted to the heat equalizer plate390 and its depending flange 94 from where it will be communicated tothe thermally-sensitive circuit-breaking arm 95. The circuitbreaking arm95 is thereby caused to flex toward the switch arm 96 because of itsthermal sensitivity, which results in the prong 99 forcing the switcharm 96 to flex rearwardly to disengage its contact from the contact onthe switch arm 97. Accordingly, the electrical circuit selectivelyenergizing the central heating element 30 is broken by the disengagementof the electrical contacts on the switch arms 96, 97 in the mannerdescribed. Excessive heating of the central heating element 30 actuatingthe safety cut-off thermostat 91 may occur due to the failure of themodulating thermostat or because the temperature-sensing bulb 81 isunable to sense a rapid temperature build-up in the central heatingelement 30 fast enough. The latter occurrence is mitigated to aconsiderable extent by the presence of the heat equalizer plate 30a.Insufficient water in the chamber 11 or excessive pressure in thechamber 11 during a steam sterilization cycle are factors which cancontribute to the acquiring of an excessive temperature by the centralheating element 30. By breaking the electrical circuit selectivelyenergizing the central heating element 30 when this excessivetemperature condition occurs, the safety cut-off thermostat 91 preventsdamage to the sterilizer and to dental and medical articles and suppliesundergoing steam sterilization in the chamber 11.

Indicator lights 92 and 93 are located on the control panel 43 adjacentthe upper margin thereof and are adapted to be illuminated forsignalling that electric power is being supplied to the sterilizer andthat the electrical heating means is energized, respectively. The powerindicator light 92, which may be red, is connected in parallel with themodulating thermostat 80 in an electric power indicator circuitunaffected by the modulation of the thermostat 80 and glows when thecontrol knob 42 is located in fill, sterilize, or vent positions so thatthe pivotal arm of switch 74 engages the contact 76. The electric powerindicator circuit for illuminating the power indicator light 92 extendsfrom one terminal of the plug 90, through the junction W, across theswitch arm 74 in engagement with the contact 76, through the terminal 83of the modulating thermostat 80, through the power indicator light 92,and then proceeds through the junction Y to return to the other terminalof the plug 90. The heat-on indicator light 93, which may be amber, isconnected in series with the modulating thermostat 80 and will thereforeglow intermittently when the control knob 42 is located in fill,sterilize, or vent positions, the illumination of the heat-on indicatorlight 93 depending upon the flow of electric current across theterminals 83, 84 of the thermostat 80 to indicate that the electricalheating means is being energized. The electric heat-on indicator circuitfor illuminating the heat-on indicator light 93 is therefore similar tothe electric power indicator circuit previously described, except thatthe electric heat- 13 on indicator circuit extends across the terminals83, 84 of 316 thermostat $11 and through the heat-on indicator light Asit is necessary to operate the sterilizer during a steam sterilizationcycle and a dry heat sterilization cycle for a predetermined period oftime in order to effect sterilization of the articles within the chamber11, a bell timer 160 (FlGURE is located on the inner surface of thefront cabinet wall behind the control panel 43, and an adjustable timercontrol knob 101 is associated therewith for setting the required timeto effect sterilization either by utilizing steam or dry heat as thesterilizing agent. The timer control knob 101 is arranged as theuppermost knob on the control panel 43, the bell 1110 sounding when thepreset time on the timer control knob 1111 has elapsed to signal thecompletion of a steam sterilization cycle or a dry heat sterilizationcycle.

It will be observed in FIGURE 4 that a partition wall 1112 extendslengthwise within the cabinet 11 between the chamber 11 and thereservoir tank 32, the partition wall 102 segregating the chamber 11from various components of the piping system and the electrical systemfor the sterilizer which are grouped on the same side of the partitionwall 162 as the reservoir tank 32. The partition wall 102 is suitablyapertured to permit the air tap line 65 and the conduit 57 to passtherethrough and may be utilized as a supporting base in which the quickconnector junctions W, X, Y, Z of the electrical system may be mountedto extend therethrough and to which other components of the pipingsystem and the electrical system may be attached. Preferably, suitableinsulation material, such as fiber glass, rock wool, or the like (notshown) is packed around the chamber 11 within the cabinet to preventexcessive heat loss from the chamber 11.

In operating the improved dual-purpose sterilizer embodying the presentinvention as a steam sterilizing apparatus, the hermetic closure door 13is opened and the control knob 42 is turned to the fill position. Thefill position of the control knob 42 allows water to enter the chamber11 from the reservoir tank 32 while causing the three heating elements30 to be energized. When water within the chamber 11 reaches a levelcovering the fill plates 41, the control knob 42 is turned to sterilizeposition. In sterilize position, both valve members A and B are in aclosed position and the flow of water from the reservoir tank 32 intothe chamber 11 is stopped, while the central heating element 30 isselectively energized under an increased power input and the sideheating elements 30 are rendered inactive. At this Point, the chamber 11is loaded with the articles to be sterilized by steam under pressure,and the closure door 13 is pivoted into a position closing the front endof the chamber 11 with the slidable bolt 15 thereon being moved intoreception within the keeper 16, as illustrated in FIGURE 1, tohermetically seal the chamber 11. The middle knob 82 on the controlpanel 43 controlling the modulating thermostat St) is then turned to aselected steam pressure and temperautre valuation. In adjusting thecontrol knob 82 for the modulating thermostat 80, the control knob 82 ispreferably turned through the indicated range of the steam sterilizationsector for steam sterilization. The operator then observes the pressuregauge 70 until the desired pressure has been obtained within the chamber11, whereupon the control knob 82 is rotated in an opposite directionaway from the extreme limit of the steam sterilization sector until theheat-on light 93 goes out, thereby setting the modulating thermostat 80to maintain the desired pressure within the chamber 11. Once thissetting of the control knob 82 has been obtained, it is not necessary toadjust the control knob 82 for subsequent steam sterilization cyclesunless it is desired to steam sterilize at a difierent pressure. Theupper timer control knob 101 is then set to the desired time for thesteam sterilization cycle.

When the period of time selected on the timer control knob 101 hasexpired, the bell 100 will ring to signal that the steam sterilizationcycle has been completed. The control knob 42 is then turned from thesterilize position to the vent position, wherein valve member A is movedto an open position while valve member B remains in a closed position,to permit steam and water within the chamber 11 to be discharged throughthe condenser tube 33 into the reservoir tank 32. The steam dischargedfrom the chamber 11 is converted to water as it passes through thecondenser tube 33 which is substantially immersed in relatively coldwater contained in the reservoir tank 32. Following the discharge ofsteam and water from the chamber 11 when the control knob 42 has beenmoved to vent position, the pressure gauge 70 will drop to register zeropressure and the hermetic closure door 13 is opened to remove thesterilized articles from the chamber 11. If it is desired to dry thesterilized articles before their removal from the chamber 11, thehermetic closure door 13 is opened slightly, and the control knob 42 isleft in vent position. As previously de scribed, the plurality ofheating elements 311 are energized under a reduced power input when thecontrol knob 42 is in vent position and supply heat for drying moisturefrom the steam sterilized articles in the chamber 11. This drying cyclefollowing the steam sterilization cycle should not be confused with adry heat sterilization cycle which must be carried on at a selected hightemperature for an extended period of time in order for sterilization totake place.

In utilizing the improved sterilizer for sterilizing ob jects, such asinstruments made of heat-resistant material and glassware, by dry heatsterilization, after the objects to be sterilized are loaded into thechamber 11, the auxiliary non-hermetic closure door 21 is insertedwithin the opening through the front cabinet wall to loosely close thechamber 11, as illustrated in FIGURE 2. The control knob 42 is turnedfrom off position directly to vent position to avoid the filP position.The middle control knob 82 for regulating the modulating thermostat isthen adjusted to a selected position within the dry heat sterilizationsector. The extreme limit at which the control knob 82 may be set in thedry heat sterilization sector may produce a temperature of 350Fahrenheit, for example. When the thermometer 27 protruding from theauxiliary non-hermetic closure door 21 registers a temperature withinthe chamber 11 sufiicient to efiect dry heat sterilization, such as 320Fahrenheit for example, the timer control knob 101 is then set for therequired time period to sterilize the objects within the chamber 11 bydry heat. At the conclusion of the dry heat sterilization cycle, thetimer bell will ring, and the auxilary door 21 can be immediatelyremoved for unloading the sterilized objects from the chamber 11.

Electric power for the sterilizer may be supplied from a standardelectrical wall socket with the heating elements 30 being energizedsimultaneously under a total input of 400 watts, or approximately 133watts for each of the three heating elements, and the centrally disposedheating element being selectively energized under a 1250 watt input.

Thus, it will be seen that we have disclosed an improved dual-purposesterilizer which may be employed in processing articles to be sterilizedby either steam sterilization or dry heat sterilization, depending uponthe nature of the articles to be sterilized and other circumstanceswhich may be involved. The operation of our improved sterilizer throughthe various cycles involved in a sterilization process requires onlysimple manipulation of the three control knobs 42, 82, and 101 on thecontrol panel 13 of the cabinet 10 and observation of the temperatureand pressure gauges 67, 70 and power and heat-on lights 92, 93 to effectsterilization by employing either steam under pressure or sustained dryheat as a sterilization agent.

In the drawings and specification there has been set 15 forth apreferred embodiment of the invention and, although specific terms areemployed, they are used in a generic and descriptive sense only and notfor purposes of limitation, the scope of the invention being defined inthe claims.

We claim:

1. A dual purpose sterilizer for dental and medical articles andsupplies or the like and adapted for selectively sterilizing by steamunder pressure or by sustained dry heat at high temperatures; saidsterilizer comprising:

(a) enclosed sterilizing chamber means including means for permittingaccess thereto for receiving articles and supplies to be sterilized andadapted to contain water when sterilizing by steam and pressure isselected;

(b) electric heating means disposed in close proximity to said chambermeans and adapted to be selectively energized to heat said chamber meansunder an increased power input for generating steam and pressure thereinwhen sterilizing by same is selected or to heat said chamber means undera reduced power input for producing sustained dry heat at hightemperatures when sterilizing by same is selected;

(c) discharge means communicating with said chamber means and adapted tobe selectively opened for discharging steam, water or air therefrom andclosed for preventing discharge therefrom; and

((1) control means operatively associated with said heating means andsaid discharge means, said control means being adapted to energize saidelectric heating means under the increased power input and to maintainsaid discharge means closed for generating steam and pressure in saidchamber means when sterilizing by same is selected and being adapted toenergize said electric heating means under the reduced power input andto open said discharge means for producing sustained dry heat at hightemperatures in said chamber means when sterilizing by same is selected.

2. A dual purpose sterilizer, as set forth in claim 1, including areservoir means adapted to contain a supply of water and communicatingwith said chamber means for supplying water thereto when sterilizing bysteam and pressure is selected, and in which said discharge meanscommunicates with said reservoir means for discharging steam and waterfrom said chamber means to said reservoir means after a sterilizingcycle by steam and pressure has been completed.

3. A dual purpose sterilizer, as set forth in claim 1, in which saidelectric heating means comprises a plurality of heating elements, and inwhich said control means is adapted to energize a single heating elementunder the increased power input when sterilizing by steam and pressureis selected and is adapted to energize all of said heating elementsunder the reduced power input when sterilizing by sustained dry heat athigh temperatures is selected.

4. A dual purpose sterilizer, as set forth in claim 1, in which saidmeans for permitting access to said chamber means comprises a primaryclosure means of high mass adapted to hermetically close said chambermeans when sterilizing by steam and pressure is selected, and asecondary closure means of limited mass adapted to be used in lieu ofsaid primary closure means when sterilizing by sustained dry heat athigh temperatures is selected to facilitate attaining high temperatureswithin said chamber means.

5. In a sterilizer,

(a) a sterilizing chamber,

(b) a reservoir tank adapted to contain water,

(c) piping means providing communication between said sterilizingchamber and said reservoir tank,

16 (d) a plurality of electric heating elements in proximity to thechamber walls for increasing the temperature within the chamber and forgenerating steam when water is contained in the chamber to 5 originate asteam sterilizing cycle,

(e) a pair of valve members alternately disposable in open positions forregulating fluid flow in said piping means between said chamber and saidtank to admit water from said tank into said chamber in beginning asterilization treatment by steam under pressure when one of said valvemembers is in open position and to discharge steam and water from saidchamber into said tank at the end of a steam sterilizing cycle when theother valve member is in open position, each of said valve members beingclosed during a steam sterilizing cycle to block communication betweensaid chamber and said tank,

(f) means operable conjointly with said valve members for selectivelyenergizing one of said heating elements under a power input when saidvalve members are closed during a steam sterilizing cycle and energizingall of said heaitng elements under a reduced power input when either ofsaid valve members is in open position,

( g) manually operable means movable between a plurality of positionsfor simultaneously controlling said valve members and said heaterenergizing means to close said valve members while actuating said heaterenergizing means for selectively energizing said one heating elementduring a steam sterilizing cycle and to alternately open each of saidvalve members in beginning and ending a steam sterilization treatmentwhile actuating said heater energizing means for energizing all of saidheating elements under a reduced power input, and

(h) said manually operable means being movable directly to the positionfor simultaneously controlling said other valve member and said heaterenergizing means to selectively open said other valve member whileactuating said heater energizing means for energizing all of saidelectrical heating elements under said reduced power input to obtain adry heat sterilizing temperature within the chamber when said chamber isempty of steam and water to provide a dry heat sterilizing cycle inresponse to the disposition of said manually operable means in saidposition.

References Cited UNITED STATES PATENTS OTHER REFERENCES Reddish:Antiseptics, Disinfectants, Fungicides and Sterilization; SecondEdition, 1957, pp. 810-818.

MORRIS O. WOLK, Primary Examiner.

E. SZOKE, J. ZATARGA, Assistant Examiners.

1. A DUAL PURPOSE STERILIZER FOR DENTAL AND MEDICAL ARTICLES ANDSUPPLIES OR THE LIKE AND ADAPTED FOR SELECTIVELY STERILIZING BY STEAMUNDER PRESSURE OR Y SUSTAINED DRY HEAT AT HIGH TEMPERATURES; SAIDSTERILIZER COMPRISING: (A) ENCLOSED TERILIZING CHAMBER MEANS INCLUDINGMEANS FOR PERMITTING ACCESS THERETO FOR RECEIVING ARTICLES AND SUPPLIESTO BE STERILIZED AND ADAPTED TO CONTAIN WATER WHEN STERILIZING BY STEAMAND PRESSURE IS SELECTED; (B) ELECTRIC HEATING MEANS DISPOSED IN CLOSEPROXIMITY TO SAID CHAMBER MEANS AND ADPATED TO BE SELECTIVELY ENERGIZEDTO HEAT SAID CHAMBER MEANS UNDER AN INCREASED POWER INPUT FOR GENERATINGSTEAM AND PRESSURE THEREIN WHEN STERILIZING BY SAME IS SELECTED OR TOHEAT SAID CHAMBER MEANS UNDER A REDUCED POWER INPUT FOR PRODUCINGSUSTAINED DRY HEAT AT HIGH TEMPERATURES WHEN STERILIZING BY SAME ISSELECTED; (C) DISHCARGE MEANS OMMUNICATING WITH SAID CHAMBER MEANS ANDADAPTED TO BE SELECTIVELY OPENED FRO DISCHARGING STEAM, WATER OR AIRTHEREFROM AND CLOSED FOR PREVENTING DISCHARGE THEREFROM; AND